Study On The Law Of Sediment Flocculation Settlement In Still Water

There are a lot of viscous fine-grained sediments in the estuary area of our country,and the viscous fine-grained sediments often flocculate.Sediment flocculation has an important impact on sediment deposition and transportation,which in turn affects estuarine and coastal geography and the surrounding environment.Therefore,studying the problem of sediment flocculation plays an important role in the migration law of pollutants in the river,the water ecological environment and river regulation and the sustainable development of the economy.Taking fine-grained sediment as the research object,this paper analyzes the kinetic model of sediment hydrostatic flocculation,the mechanism of temperature’s influence on sediment flocculation and the settlement law of large-sized flocs through theoretical deduction and physical experiments.The main research contents and results are as follows:(1)Based on the DLVO theory,the expressions of attraction and repulsion between particles were solved,and the conditions for flocculation were determined,that is,whether the sediment particles crossed the position of the potential barrier as the standard;by introducing the spherical flocculation development model and applying Fick’s first law,Taking into account the resistance of the sediment particles,the kinetic equation of sediment flocculation and the flocculation rate coefficient under still water conditions are deduced,and the parameters such as the half-life period of the flocculation process and the flocculation average settling velocity are obtained.,the flocculation kinetic equation derived in this paper is in good agreement with the experimental data.(2)Based on the self-designed fine-grained sediment thermal insulation sedimentation test platform,the sedimentation law of the interface between clear and muddy sediments was observed under the conditions of sediment concentration of 60g/L,temperature of 4° to 35°,and different electrolyte concentrations.The study found that with the increase of temperature,the sedimentation velocity of the clear-muddy interface will gradually increase.Based on the flocculation rate coefficient deduced in Chapter 3,the influence of temperature on parameters such as diffusion coefficient and potential barrier height is considered,and it is theoretically proved that temperature plays a role in promoting sediment flocculation.(3)The settling process of floc particles was recorded by high-speed photography,and the motion parameters of flocs were obtained by image processing software such as Adobe Photoshop CS6,Image-pro plus and MATLAB,and the settling laws of large-size flocs under still water conditions were obtained.The test results show that for large-sized flocs with particle sizes ranging from 0.17 mm to 0.45 mm and 0.17 mm to 0.66 mm,the sedimentation velocity and particle size satisfy a good linear relationship.(4)Taking the single particle of sediment outside the floc as the research object,fully considering the inter-particle force,it is believed that the failure of the floc is mainly caused by the shear force of the water flow,and its expression can be obtained according to Newton’s law of internal friction.And under the condition of particle force balance,according to the relationship between the cohesive force between particles and the shear force of water flow,the settling velocity formula of large size flocs under hydrostatic condition is established.